This invention relates to a novel class of compounds which exhibit analgesic activity upon parenteral administration.
Recently, endogenous substances having morphine-like properties have been extracted from mammalian brain or csf. These substances, named enkephalin, have been identified by Hughes et al., Nature, 258, 577 (1975) as pentapeptides having the following sequences: EQU H-Tyr-Gly-Gly-Phe-Met-OH EQU H-Tyr-Gly-Gly-Phe-Leu-OH.
These compounds are referred to as methionine-enkephalin and leucine-enkephalin, respectively.
Although these compounds have been shown to exhibit analgesic activity in mice upon administration intracerebroventricularly [Buscher et al., Nature, 261, 423 (1976)], they are practically devoid of any useful analgesic activity when administered parenterally.
A novel class of compounds has now been discovered. These compounds exhibit significant and demonstrable analgesic activity when administered systemically. It is to this class of compounds that this invention is directed.